Original Research PaperSolvent-free synthesis of Cu-Cu2O nanocomposites via green thermal decomposition route using novel precursor and investigation of its photocatalytic activity
Graphical abstract
Introduction
Dyes are unavoidable chemicals in some industries especially textile [1], but most of them pose a potential threat to aquatic creatures and human beings, detrimental to the environment and aquatic creatures if directly poured into water without proper treatment [2]. However, conventional approaches to treat wastewater including coagulation–flocculation [3], membrane separation [4], and adsorption [5], [6] determined to be insufficient or exhibit drawbacks [7], such as producing a more concentrated pollutant-containing phase, are unsatisfactory for purifying the wastewater after textile dyeing and washing [8]. Thus, the development of green and inexpensive technologies for environmental remediation is highly desired [9].
In the past few years, photocatalysis has attracted much attention as a new and efficient method to treat wastewater containing colorants. Semiconductor-based photocatalysts such as titanium dioxide (TiO2) and zinc oxide (ZnO) have been greatly studied [10], [11] and absorption of only a small fraction of sunlight (ultraviolet or near ultraviolet) due to their broad band gap (3.0–3.2 eV) is the most important disadvantage of them. Therefore, development of photocatalysts which can efficiently utilize sunlight is an urgent scientific research scope. Cuprous oxide (Cu2O) as a p-type semiconductor having a direct band gap of 1.9–2.2 eV can absorb a large part of visible light (λ < 620 nm) and is a promising photocatalyst to break down dyes [12], [13]. However, photoelectrons easily tend to recombine with holes in Cu2O-based photocatalysts, which leads to the limitation of their photocatalytic activities [14]. According to the previous studies, the heterojunction of Cu and Cu2O can enhance the photocatalytic property of Cu2O-based semiconductors, because the existence of Cu can promptly transfer photoelectrons, avoiding the recombination of electron–hole pairs [15]. Thus, Fabrication of Cu/Cu2O (metal/semiconductor) nanocomposites are of interest for photocatalysis [16], [17], [2].
Different morphologies of Cu/Cu2O nanocomposites such as flowers, spheres, cubes, hexapods, wires, and hollow structures have been synthesized by solvothermal [17], wet chemical [18], [19], hydrothermal [20], [21], electrochemical deposition [22], ball milling [23] and microemulsion method [24]. Nonetheless, in all mentioned methods, presence of an appropriate reductant for reducing Cu2+ to Cu and Cu+ is essential and in addition, to ensure the formation of composite, final calcination step is unavoidable and so these methods should be carried out in two-step. In the present work, in order to develop an efficient photocatalyst that can sufficiently utilize solar energy, Cu-Cu2O nanocomposites were synthesized via a green, single step and reductant-free solid-state thermal decomposition route using pomegranate marc peel dyes (PMP)-Cu(II) as a new copper source, for the first time. It has been proved that pomegranate peel is a rich source of different pigments such as phenolics, proanthocyanidins and flavonoids which can be extracted [25] and so, we extracted the pomegranate peel pigments by Cu2+ ions. Effect of various parameters including reaction time, temperature and precursor type on composition and morphology of final products were well studied. The photocatalytic activity of obtained nanocomposites was evaluated using methylene blue (MB) as a model of organic pollutant under visible light irradiation.
Section snippets
Materials and characterization
All the chemical reagents were of analytical grade and were used as received without any further purification. The Pomegranate marc Peels (PMP) were collected and washed thoroughly with water to remove any impurities. After drying at room temperature, the samples were ground into powder by means of grinder. The crystal structural and compositional properties of products were recorded by X-ray diffraction (Philips-X’PertPro) and FT-IR (Magna-IR, spectrometer 550 Nicolet with 0.125 cm−1 resolution
Results and discussion
Crystalline structure and phase purity of as-prepared products have been determined using XRD. Fig. 1a–c show XRD patterns of samples S1-S3 prepared using PMP-Cu(II) as starting reagent, respectively. According to Fig. 1a and b, the samples S1 and S2 are found to be composite materials, which are characterized by two sets of diffraction peaks which can be indexed to cubic phase of Cu2O (JCPDS No. 78–2076, space group: Pn-3 m and calculated cell parameter a = 4.2670 Å) and cubic phase of Cu (JCPDS
Conclusion
In summary, Cu-Cu2O binary nanocomposites were successfully prepared via a novel, facile and solvent-free solid state thermal decomposition route using PMP-Cu(II), as a novel starting reagent for the first time. Effect of reaction parameters such as time, temperature and precursor type on product composition and morphology was well studied. The results showed by using PMP-Cu(II) as precursor, Cu-Cu2O nanocomposites with good uniformity and crystallinity will be obtained even in absence of argon
Acknowledgments
This work was supported by the Chemistry Research Center at Islamic Azad University, Arak branch, Arak, Iran.
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